1. Field of the Invention
The present invention relates to transfer films, methods for manufacturing film sensors, film sensors, sensors integrated with front panel (front panel and sensor assemblies), and image display devices. Specifically, the invention relates to a front panel and sensor assembly serving as a capacitive input device that can detect a finger touch position as a change in capacitance, to a film sensor that can be used in such a sensor assembly, to a transfer film used for the manufacture of a film sensor, to a method for manufacturing a film sensor using such a transfer film, and to an image display device including a sensor integrated with front panel.
2. Description of the Related Art
Recently, there have been various types of electronic equipment, such as cellular phones, car navigation systems, personal computers, ticket machines, and banking terminals, in which a tablet-type input device is disposed on a surface of a display device such as a liquid crystal device. A user views an instruction image displayed in the image display region of the liquid crystal device and touches the position where the instruction image is displayed, for example, with a finger or touch pen, thereby inputting information associated with the instruction image. The liquid crystal display window of such electronic equipment is equipped with a cover glass for protection. Conventionally, this cover glass has a frame-shaped black light-shielding layer formed on the peripheral portion of the back surface of a transparent glass substrate.
Touch panels are often used in the electronic equipment mentioned above. Whereas resistive touch panels are currently predominant, there is a growing need for capacitive touch panels since they support multi-touch function, which allows an image to be zoomed in and out by gestures such as tapping, flicking, and pinching on the screen with finger tips, and also provide good visibility and durability. In particular, a need exists for capacitive touch panels including thinner sensors. There will therefore be a growing market for cover glass and sensor assemblies including a capacitive film sensor bonded to the back surface of a cover glass, such as that disclosed in Japanese Unexamined Patent Application Publication No. 2012-133597 (Patent Literature 1).
Patent Literature 1 discloses a cover glass and sensor assembly including a cover glass for an electronic equipment display window and a capacitive film sensor bonded to the back surface of the cover glass. The cover glass has a first frame-shaped light-shielding layer formed on the peripheral portion of the back surface of a transparent glass substrate by screen printing. The film sensor includes a transparent substrate sheet; a transparent conductive layer that is formed on each surface of the substrate sheet and that has an electrode pattern in a central window region and a fine routing circuit pattern in an outer frame region; a light-shielding conductive layer that is formed on the fine routing circuit pattern of each transparent conductive layer and that has the same width as the fine routing circuit pattern; an anticorrosive functional layer that is formed on each surface of the substrate sheet on which the transparent conductive layer and the light-shielding conductive layer are formed and that covers the portion of the outer frame region other than a terminal portion; and a second frame-shaped light-shielding layer formed on the peripheral portion of the front surface of the substrate sheet on which the transparent conductive layer, the light-shielding conductive layer, and the anticorrosive functional layer are formed. The second frame-shaped light-shielding layer is formed by exposing and developing a color resist material. The inner edges of the second frame-shaped light-shielding layer are located closer to the center than the inner edges of the first frame-shaped light-shielding layer. Patent Literature 1 discloses that this structure provides a cover glass and sensor assembly having a display screen with sharp contours, good visibility, and high visual integrity with the portion around the display screen as viewed through the cover glass.
Japanese Unexamined Patent Application Publication No. 2013-228695 (Patent Literature 2) discloses a black resin layer containing a black pigment, an alkali-soluble polymeric compound, an ethylenically-unsaturated-bond containing compound, and a photopolymerization initiator. The black resin layer has a bulk strength of 100 N/1.6 mmφ (where φ is the diameter) or more after heating at 240° C. for 80 minutes and then heating at 300° C. for 30 minutes.
Patent Literature 2 also discloses a method for manufacturing such a black resin layer. This method includes the steps of applying to a substrate a photosensitive resin composition containing a black pigment, an alkali-soluble polymeric compound, an ethylenically-unsaturated-bond containing compound, and a photopolymerization initiator; exposing the photosensitive resin composition on the substrate; developing the exposed photosensitive resin composition; and performing post-exposure after the development step. This method satisfies condition (A) or (B):
Condition (A): the photopolymerization initiator is an α-aminoalkylphenone or α-hydroxyalkylphenone.
Condition (B): the post-exposure after the development step is performed both on a surface of the photosensitive resin composition that is in contact with the substrate and on a surface of the photosensitive resin composition that is not in contact with the transparent substrate.
Patent Literature 2 also discloses a method for manufacturing a capacitive input device having a front panel and, on a noncontact side of the front panel, at least elements (1) to (4):
(1) a decorative member manufactured by the above method for manufacturing a black resin layer;
(2) a plurality of first transparent electrode patterns extending in a first direction, each composed of a plurality of pads connected through connections;
(3) a plurality of second electrode patterns electrically insulated from the first transparent electrode patterns and extending in a direction crossing the first direction, each composed of a plurality of pads; and
(4) an insulating layer electrically insulating the first transparent electrode patterns from the second electrode patterns.